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R.C. Stone and G.L. Hammer

Agricultural Production Systems Research Unit, Qld Department of Primary Industries and CSIRO, PO Box 102, Toowoomba, Qld 4350


In north-east Australia climatic influences and their associated risks impact heavily on yields of winter and summer crops. To improve farm profitability and reduce risk in this environment, analyses incorporating crop simulation models indicate that substantial improvements in gross margins/profits are possible through changes in management based on a seasonal forecast. Appropriate tactical management techniques involving seasonal forecasting of rainfall and frost likelihood may help reduce losses in the potentially bad years, and aid the maximising of returns in the potentially good years.


We applied a probabilistic seasonal forecast system based on pattern analysis of Southern Oscillation Index behaviour using SOI phases (2). Lagged probability distributions of rainfall or date of first or last frost corresponding to each of five SOI phases can be generated for any location that has sufficient data. The value of application of SOI phase-based management decision options, such as N fertiliser rate and cultivar maturity type was addressed through incorporation of the SOI phase system into crop simulation models (1). Further inclusion of economic and risk analyses allowed relative advantages of appropriate tactical decision options over long-term best-bet strategies to be assessed.


In general, there is a higher likelihood of any given amount of rain and a lower risk of a late damaging frost in winters following SOI phases consistently positive or rapidly rising in late autumn. Conversely, there is a decreased likelihood of any given amount of rain and an increased risk of a late damaging frost following SOI phases consistently negative or rapidly falling in late autumn. Reliable forecasts of first and last frost probability are also possible from the end of February. Potential yield was similarly related to SOI phase. For example, for late wheat (1 June sowing, N unlimiting), clusters of yield distributions were related to whether the SOI phase in the previous autumn was SOI rapidly-falling or SOI rapidly-rising. Switching to a tactical approach instead of a long-term strategic approach reduces risk of making a loss through use of a rainfall forecast and improves average profit by $10-20/ha per annum. Further adjustment of the tactical approach which utilises frost forecasts results in a further reduction in risk and additional average profit improvement of $10/ha. However, the results can be higher or lower in individual years.


1. Hammer, G.L., Woodruff, D.R. and Robinson, J.B. 1987. Agric. For. Meteorol, 41, 123-142.

2. Stone, R.C., and Auliciems, A. 1992. Int. J. Climatol. 12, 625-636.

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